1. Field of the Invention
The present invention relates to an apparatus and method for generating a supply voltage for a power amplifier in a power supply modulator. More particularly, the present invention relates to an apparatus and method for improving an efficiency of the power supply modulator for modulating a supply voltage for the power amplifier.
2. Description of the Related Art
With the development of wireless communication technologies there has been an increase in consumer use of various multimedia signals, and an interest in Fourth-Generation (4G) communication systems is rapidly increasing according to the need for rapid transmission of the various multimedia signals in mobile environments.
4G communication systems provide a higher transmission rate, a wider bandwidth, and a higher Peak to Average Power Ratio (PAPR) than other communication systems, for example, 3rd Generation (3G) communication systems. 4G communication systems use a power supply modulation amplifier that amplifies an input signal by using a supply voltage that is modulated according to an amplitude of the input signal. For example, the power supply modulation amplifier may use an Envelope Elimination and Restoration (EER) amplification technique, an Envelope Tracking (ET) amplification technique, a polar amplification technique, or any other similar and/or suitable amplification technique.
FIG. 1 illustrates a block configuration of a power supply modulation amplifier according to the related art.
Referring to FIG. 1, when the ET amplification technique is used, the power supply modulation amplifier is configured as illustrated in FIG. 1. A Related art power supply modulation amplifier includes a baseband signal processor 100, a power supply modulator 110, a Radio Frequency (RF) processor 120, and a power amplifier 130. The baseband signal processor 100 generates and outputs In-phase Quadrature (IQ) data. The RF processor 120 converts the IQ data received from the baseband signal processor 100 into an RF signal, and provides the RF signal as an input signal of the power amplifier 130.
The power supply modulator 110 determines a supply voltage of the power amplifier 130 according to an envelope corresponding to the IQ data received from the baseband signal processor 100. That is, the power supply modulator 110 generates the supply voltage based on an amplitude of a signal inputted to the baseband signal processor 100. The power amplifier 130 amplifies the input signal received from the RF processor 120 by using the supply voltage received from the power supply modulator 110 and then outputs the amplified input signal.
As described above, when the power supply modulation amplifier amplifies the input signal by using the supply voltage modulated according to the amplitude of the input signal, an envelope of an RF output signal of the power supply modulation amplifier is determined by the supply voltage modulated according to the amplitude of the input signal. Thus, the linear modulation performance of the power supply modulator 110 directly affects the quality of the RF output signal.
Therefore, there is a need for a communication system having a power supply modulator with a good linear modulation performance in order to increase the power amplification efficiency of the power supply modulation amplifier.